[1]} show that the optimal, valid and order-coherent
belief update \(\psi \)  is the probability measure \(\nu (d\theta \,d\varphi )\)  minimising the loss
\(L(\nu ; Y,Z,\pi _0)=\int l(\varphi , \theta ;Y,Z,\pi _0) \nu (d\theta \, d\varphi )+KL(\nu ||\pi _0)\) 
